Australia produces ~6% of the worlds coal [0]. That is the only thing nature could care about; figures like % exports and per capita numbers are meaningless. 6% is a big enough slice of the pie for everyone to argue about. The 34% figure specifically is a bit meaningless because it is by value and there is big price (about x4?) difference between met coal (Queensland) vs. thermal coal (NSW). It doesn't make sense to try and compare Australian met coal exports to, say, Indonesian thermal.

Also as a counter argument, attempting to pressure China economically by choking their imports would probably end badly for us.

[0] https://en.wikipedia.org/wiki/List_of_countries_by_coal_prod...